Historically, analysis performed by engineers is one step in the long process in the attempt to simulate and verify real-world expected performance of engineered products. Complete models containing information such as geometry, material properties, loads and analysis type are entered into an analysis program and basic results such as displacements are calculated. These values can then be compared to predetermined limits of the material, whether isotropic, orthotropic, or anisotropic, to locate any critical areas in the model. Areas of the model that exceed any specified limit need to be reconfigured to obtain positive margins of safety, although a majority of the time, areas of high margin of safety are left unchanged or not optimized. Iterations such as changing the material or component geometry can reduce the margin of safety. This process is both lengthy and not very cost effective.
A method known as Volumetrically Controlled Manufacturing (VCM) can assist in reducing cost, time to manufacturing, and margins of safety. VCM is described in U.S. Pat. Nos. 5,796,617 and 5,594,651, the contents of which are incorporated herein. VCM may be applied, for example, to an orthopedic procedure known as THA (Total Hip Anthroplasty). This procedure involves replacing a patient's hip with a hip stem so as to maintain the patient's physiological capability of normal walking motion. Traditional analysis revealed a couple of areas of high stresses that an isotropic material displaced onto surrounding bone and caused pain in the patient and premature failure of that same bone structure, prompting post-THA surgery. The problem that arose involved using a configuration and material that was much stiffer than what it replaced. Attempts at reducing the stiffness involved using composite materials. These attempts however failed due to inter-laminar shear causing delamination, and secondarily matrix/fiber disbonding. These failures occurred due to an inability to come up with a ply configuration that could withstand the load environment and unique structural properties of bone.
In order to provide an efficient analysis tool to determine the optimum material properties for an engineered product such as a hip stem, a different approach from traditional analysis had to be made. The VCM process encompasses this new approach. Instead of determining the displacements, stresses and strains in a product using traditional analysis methods, through real world testing, displacements are recorded and entered into the analysis. The material properties are now the unknowns and are solved for.
As described in greater detail below the material properties may be solved for in an iterative analysis process. The analysis continues until specified elements display displacements all within a specified tolerance. In this way, an iteration process continues until convergence, thereby, optimizing the entire model for its particular environment and loading condition. This plays very much into the use of composite materials because they can be tailored in many different ways to come up with the desired material property, unlike isotropic metallics that have less tailorability in comparison to composites.
The optimization may also be extended to control the type of solutions that result from the above-described processing. For example, the system may be constrained to find a solution in which the finite volume elements (“voxels”) that make up the object have certain symmetries. By way of illustration, the system may be constrained to find a solution in which the voxels are isotropic or are transversely isotropic. Imposing such symmetries on the solutions improves manufacturability by defining each voxel in terms of properties (e.g., Poisson's ratio, Young's modulus) that are the same, or that have certain symmetries, throughout the voxel. In some implementations, the system may be configured to generate solutions for isotropic voxels, transversely isotropic voxels, and for anisotropic voxels. The actual solution used for manufacturing may be chosen based on the relative ease of controlling manufacturing equipment to produce the desired object.
As mentioned above, composite materials are useful for VCM because they can be tailored in many different ways to come up with the desired material property. A composite material is a combination of two or more materials in which the individual materials remain separate on a macroscopic level. One way to construct a composite material is to laminate structural fibers in appropriate matrices compatible with these fibers. As described in greater detail below, the matrices in which the fibers are incorporated may be modified to include certain “impurities”. In the case of a THA, for example, the impurities may be biologic material, bone, crushed bone, co-factors, biological cells, bio-active materials, medications, antibiotics, radioactive materials, etc.